1. Field of the Invention
This invention relates to database managing apparatuses and database record retrieving apparatuses, and particular to a database managing apparatus which makes a database file in which compressed requested records are stored and to a database record retrieving apparatus which extracts a requested record from a memory medium in which a database file is stored.
2. Related Art
Recently, databases have been used in, for example, a vehicular navigation system as a map database or a telephone number database for setting a destination. The telephone number database includes several attributions of a shop or a company including: a name, a telephone number, an address, and position data (the longitude, the latitude, the altitude). When a driver of a vehicle inputs a search key such as a telephone number of a shop as a destination, the database is searched. When a record corresponding to the search key exists in the database, the navigation system extracts (retrieves) one article data (each attribution) to which the record belongs, and displays information regarding the one article data or uses as the destination.
Here, since the above-described databases including the map database and the telephone number database are generally stored in one common storing medium such as one CD-ROM, an amount of total data of each database is naturally limited. Therefore, the records to be stored are generally stored in the CD-ROM after being compressed (encoded) so as to reduce a size. When the records are read out from the database to be used in a process, the records are restored (decoded) by being decompressed to a former condition.
Here, in a conventional database managing apparatus, the data is compressed by a unit of record as a whole. Therefore, when the database is searched, it needs to decompress by a unit of the record as a whole before searching the database file. In general, the size of a main memory of the CPU for performing the data compression, the data compression, or the search process, is approximately 10 MB (mega bytes). However, a size of the total records in the database is approximately 100 MB. Therefore, when the CPU performs the search process, the CPU needs to repeat a series of processes including:
(1) loading (reading out) parts of the compressed data from the CD-ROM to the main memory;
(2) decompressing the loaded compressed data to restore it; and
(3) searching the restored data.
Hence, it takes long time to complete searching for one article record.
Furthermore, in a relation model database, which has plural attributions for one article, a projection may be performed. The projection retrieves only a particular record having a desired attribution (field). In such a case, it also needs to restore entire records to obtain only the particular record belonging to one attribution.